Hi,
This Patch set adds migration support for VFIO devices in QEMU.
This Patch set include patches as below:
Patch 1-3:
- Define KABI for VFIO device for migration support for device state and newly
added ioctl definations to get dirty pages bitmap. These 3 patches are same as
the first 2 patches in kernel patch set.
Patch 4-6:
- Few code refactor
- Added save and restore functions for PCI configuration space
Patch 7-12:
- Generic migration functionality for VFIO device.
* This patch set adds functionality only for PCI devices, but can be
extended to other VFIO devices.
* Added all the basic functions required for pre-copy, stop-and-copy and
resume phases of migration.
* Added state change notifier and from that notifier function, VFIO
device's state changed is conveyed to VFIO device driver.
* During save setup phase and resume/load setup phase, migration region
is queried and is used to read/write VFIO device data.
* .save_live_pending and .save_live_iterate are implemented to use QEMU's
functionality of iteration during pre-copy phase.
* In .save_live_complete_precopy, that is in stop-and-copy phase,
iteration to read data from VFIO device driver is implemented till pending
bytes returned by driver are not zero.
Patch 13:
- Add vfio_listerner_log_sync to mark dirty pages. Dirty pages bitmap is queried
per container. All pages pinned by vendor driver through vfio_pin_pages
external API has to be marked as dirty during migration.
When there are CPU writes, CPU dirty page tracking can identify dirtied
pages, but any page pinned by vendor driver can also be written by
device. As of now there is no device which has hardware support for
dirty page tracking. So all pages which are pinned by vendor driver
should be considered as dirty.
In Qemu, marking pages dirty is only done when device is in stop-and-copy
phase because if pages are marked dirty during pre-copy phase and content is
transfered from source to distination, there is no way to know newly dirtied
pages from the point they were copied earlier until device stops. To avoid
repeated copy of same content, pinned pages are marked dirty only during
stop-and-copy phase.
Patch 14:
- With vIOMMU, IO virtual address range can get unmapped while in pre-copy
phase of migration. In that case, unmap ioctl should return pages pinned
in that range and QEMU should report corresponding guest physical pages
dirty.
Patch 15:
- Make VFIO PCI device migration capable. If migration region is not provided by
driver, migration is blocked.
Yet TODO:
Since there is no device which has hardware support for system memmory
dirty bitmap tracking, right now there is no other API from vendor driver
to VFIO IOMMU module to report dirty pages. In future, when such hardware
support will be implemented, an API will be required in kernel such that
vendor driver could report dirty pages to VFIO module during migration phases.
Below is the flow of state change for live migration where states in brackets
represent VM state, migration state and VFIO device state as:
(VM state, MIGRATION_STATUS, VFIO_DEVICE_STATE)
Live migration save path:
QEMU normal running state
(RUNNING, _NONE, _RUNNING)
|
migrate_init spawns migration_thread.
(RUNNING, _SETUP, _RUNNING|_SAVING)
Migration thread then calls each device's .save_setup()
|
(RUNNING, _ACTIVE, _RUNNING|_SAVING)
If device is active, get pending bytes by .save_live_pending()
if pending bytes >= threshold_size, call save_live_iterate()
Data of VFIO device for pre-copy phase is copied.
Iterate till pending bytes converge and are less than threshold
|
On migration completion, vCPUs stops and calls .save_live_complete_precopy
for each active device. VFIO device is then transitioned in
_SAVING state.
(FINISH_MIGRATE, _DEVICE, _SAVING)
For VFIO device, iterate in .save_live_complete_precopy until
pending data is 0.
(FINISH_MIGRATE, _DEVICE, _STOPPED)
|
(FINISH_MIGRATE, _COMPLETED, STOPPED)
Migraton thread schedule cleanup bottom half and exit
Live migration resume path:
Incomming migration calls .load_setup for each device
(RESTORE_VM, _ACTIVE, STOPPED)
|
For each device, .load_state is called for that device section data
|
At the end, called .load_cleanup for each device and vCPUs are started.
|
(RUNNING, _NONE, _RUNNING)
Note that:
- Migration post copy is not supported.
v8 -> v9:
- Split patch set in 2 sets, Kernel and QEMU sets.
- Dirty pages bitmap is queried from IOMMU container rather than from
vendor driver for per device. Added 2 ioctls to achieve this.
v7 -> v8:
- Updated comments for KABI
- Added BAR address validation check during PCI device's config space load as
